Automatic transmission planetary gear carrier assemblies commonly employ rotatable thrust washers between a planet gear and an associated gear carrier flange. The thrust washers provide a reaction surface for thrust loads generated by the transmission of torque between the planet gear and meshing sun and ring gears.
In planetary gear assemblies for automobile transmissions, thrust washers, in addition to sustaining the applied thrust loads, will ideally facilitate a flow of lubricant reaching a bearing surface of the planet gear and a shaft on which the planet gear rotates. It is also desirable for the design of the thrust washers to facilitate assembly of the planet carrier.
Well known are thrust washers which pilot on an outside diameter of the shaft on which the planet gear rotates. The piloting relationship between the shaft and the thrust washer, however, inhibits oil flow between them. Additionally, the washers and the gear must be individually aligned with a shaft when placing them on the shaft.
It is also known to provide a channel in the carrier flange on a side proximate to the washer extending radially inward from the shaft. Such a channel by itself is largely ineffective in providing lubricant to the bearing surfaces of the planet gear and the shaft and an interposed needle roller bearing because there is little radial space between the thrust washer and the shaft when the thrust washer pilots on the shaft.
It is further known to provide the planet gears or the thrust washers with channels in respective facing surfaces to facilitate lubricant flow to the bearing surface. The channels, however, reduce surface area between the gear thrust surface and the thrust washer, resulting in a higher load per unit of area between the gear and the thrust washer.
It is yet further known to provide thrust washers with a plurality of notches at their inside diameters in combination with a channel in the carrier flange. These notches and the piloting portions between the notches form a cloverleaf pattern at the inside diameter of the washer, allowing lubricant to pass to the bearing surface when one of the notches overlaps the channel in the carrier. However, if a piloting portion of the washer overlaps the channel, the flow of lubricant to the shaft would be blocked much as if there were no notches at the thrust washer inside diameter. Also, when two such thrust washers are used together, the piloting portion of one washer may overlap the notches of the other washer, resulting in the same minimal flow to the bearing surface as if a washer with no relief notches were used.